1. Field of the Invention
The instant invention relates generally to portable lighting devices such as battery-powered flashlights and lanterns, and particularly to a built-in device for indicating the level of charge or capacity of the batteries contained therein.
2. Discussion of the Related Art
Flashlights and a majority of portable lanterns are battery-operated using either non-rechargeable or rechargeable batteries. One problem commonly associated with these batteries is determining the useful or remaining life of the battery. If the batteries are already in a flashlight or portable lantern, the quickest way to determine the strength of the battery is by turning the flashlight or lantern on. If the incandescent or fluorescent lamp illuminates, most individuals are satisfied that the batteries are good. However, if the flashlight or portable lantern does not illuminate, then the question is whether the problem lies in the batteries or the lamp. The user must then either replace the batteries in the flashlight with new batteries and/or the lamp, or remove the existing batteries and/or the lamp and test them.
Several devices have been developed for testing batteries to determine the freshness or state-of-charge of the cell. For example, U.S. Pat. Nos. 4,723,656 and 5,128,616 disclose a blister-type package for new batteries with a battery condition indicator built into the blister portion of the package. The blister can be deformed to place the tester across the terminals of the battery to be tested. The tester employs a thermochromic material in combination with a resistive element. The flow of current produces a temperature gradient across the resistive element which, in turn, causes a color change in the thermochromic material to indicate the state-of-charge of the battery. As mentioned, the testers are associated with the package in which the batteries are purchased. Once the batteries are removed from the package, the package is usually discarded and from then on the state-of-charge of the battery is indeterminate.
U.S. Pat. Nos. 4,702,563, 4,702,564, 4,726,661, and 4,737,020, disclose a flexible battery tester which has a conductive circuit pattern associated with a layer of thermochromic material. The flexible member is bent so that the circuit pattern can contact the positive and negative terminals of the battery to be tested and, again, the temperature gradient is observed in the thermochromic material and correlated with the state-of-charge of the battery. All of these testers suffer from the same deficiency in that the tester is a separate element, which in the case of the package, is usually thrown away, and in the case of the above patents, can be lost or misplaced. In either event, the state-of-charge of the battery is indeterminate once the testing device is no longer available.
U.S. Pat. No. 4,876,632 discloses a flashlight containing a device for indicating the level of charge on a battery. The battery life indicator is a module that is mounted between the flashlight head or lamp assembly containing the light reflector and a battery housing assembly for holding the batteries. The battery life indicator module contains an indicator, such as a light-emitting diode (LED). Internal to the battery life indicator module is a circuit which measures the battery level and activates the indicator to display the battery level. The module also provides the necessary electrical connection between the batteries and the light lamp of the flashlight. The battery life indicator is activated by the On/Off switch of the flashlight so that the power is not drained when the flashlight is not in use. However, when the flashlight is turned on, the battery-life indicator module and its associated circuit are also powered and remain on while the flashlight is on. In the event the flashlight lamp burns out, and the operator fails to notice that the battery-life indicator is activated, the tester will result in a discharge of the batteries.
U.S. Pat. No. 4,962,347 discloses a battery-powered flashlight or portable lantern having a built-in device for determining the strength, voltage or capacity of the batteries. The flashlight or lantern includes a housing which holds the batteries and which receives an electrically powered light source mounted thereon which is energized by the batteries. A battery-testing circuit is mounted in the housing having a display which is detectable from the outside of the housing. A three-way switch mounted in the housing is placed in a first position to connect the light source with the batteries, and in a second position to connect the battery-testing circuit with the batteries, and a third position to disconnect the batteries from both of the light and the battery-testing circuit.
U.S. Pat. No. 4,432,041 discloses a portable lighting device which includes circuitry for detecting a low voltage condition of the batteries. Upon the detection of a low voltage condition, the circuitry provides an intermittent sound that is indicative of the low voltage condition. A disadvantage associated with this circuitry is that the tester is constantly "ON" in order to monitor the voltage level. Furthermore, the tester circuitry only provides an indication when the voltage level of the batteries are below a certain level. There is no indication as to the remaining life of the battery and the state-of-charge of the battery is indeterminate.
In view of these disadvantages, a battery tester forming an integral part of the flashlight housing which is not in series with a circuit operating the flashlight is desired.